Optical bypass method and architecture

ABSTRACT

The invention pertains to optical fiber transmission networks, and is particularly relevant to transmission of high volume of data and voice traffic among different locations. In particular, the improvement teaches improvements to an optical transport system to allow for efficient and flexible network evolution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Application Ser. No.60/386,084 entitled “Optical Bypass Method and Architecture”, by Young,filed Jun. 4, 2003.

FIELD OF THE INVENTION

The present invention relates, in general, to the field of opticalcommunications, and in particular to optical fiber transmissionnetworks. The invention is particularly relevant to transmission of highvolume of data and voice traffic among different locations. Inparticular, the invention teaches improvements to an optical transportsystem to allow for efficient and flexible network evolution. Theinvention teaches a method and architecture for bypassing a terminalsite without affecting existing traffic.

BACKGROUND OF THE INVENTION

A goal of many modern long haul optical transport systems is to providefor the efficient transmission of large volumes of voice traffic anddata traffic over trans-continental distances at low costs. Variousmethods of achieving these goals include time division multiplexing(TDM) and wavelength division multiplexing (WDM). In time divisionmultiplexed systems, data streams comprised of short pulses of light areinterleaved in the time domain to achieve high spectral efficiency, highdata rate transport. In wavelength division multiplexed systems, datastreams comprised of short pulses of light of different carrierfrequencies, or equivalently wavelength, are co-propagate in the samefiber to achieve high spectral efficiency, high data rate transport.

The transmission medium of these systems is typically optical fiber. Inaddition there is a transmitter and a receiver. The transmittertypically includes a semiconductor diode laser, and supportingelectronics. The laser is often a DFB laser stabilized to a specifiedfrequency on the ITU frequency grid. The laser may be directly modulatedwith a data train with an advantage of low cost, and a disadvantage oflow reach and capacity performance. In many long haul systems, the laseris externally modulated using a modulator. A single stage modulator issufficient for a non-return-zero (NRZ) modulation format. A two stagemodulator is typically used with the higher performance return-to-zero(RZ) modulation format. An example of a modulator technology is theMach-Zehnder lithium niobate modulator. Alternatively, anelectro-absorptive modulator may be used. After binary modulation, ahigh bit may be transmitted as an optical signal level with more powerthan the optical signal level in a low bit. Often, the optical signallevel in a low bit is engineered to be equal to, or approximately equalto zero. In addition to binary modulation, the data can be transmittedwith multiple levels, although in current optical transport systems, atwo level binary modulation scheme is predominantly employed. Thereceiver is located at the opposite end of the optical fiber, from thetransmitter. The receiver is typically comprised of a semiconductorphotodetector and accompanying electronics.

Typical long haul optical transport dense wavelength divisionmultiplexed (DWDM) systems transmit 40 to 80 10 Gbps (gigabit persecond) channels across distances of 1000 to 6000 km in a single 30 nmspectral band. In a duplex system, traffic is both transmitted andreceived between parties at opposite end of the link. In a DWDM system,different channels operating at distinct carrier frequencies aremultiplexed using a multiplexer. Such multiplexers may be implementedusing array waveguide grating (AWG) technology or thin film technology,or a variety of other technologies. After multiplexing, the opticalsignals are coupled into the transport fiber for transmission to thereceiving end of the link. The total link distance may in today'soptical transport systems be two different cities separated bycontinental distances, from 1000 km to 6000 km, for example. Tosuccessfully bridge these distances with sufficient optical signal powerrelative to noise, the signal is periodically amplified using an in lineoptical amplifier. Typical span distances between optical amplifiers are50-100 km. Thus, for example, 30 100 km spans would be used to transmitoptical signals between points 3000 km apart. Examples of inline opticalamplifiers include erbium doped fiber amplifiers (EDFAs) andsemiconductor optical amplifiers (SOAs).

At the receiving end of the link, the optical channels are demultiplexedusing a demultiplexer. Such demultiplexers may be implemented usingarray waveguide (AWG) technology or thin film technology, or a varietyof other technologies. Each channel is then optically coupled toseparate optical receivers.

Other common variations include the presence of post-amplifiers andpre-amplifiers just before and after the multiplexer and de-multiplexer.Often, there is also included dispersion compensation with the in lineamplifiers. These dispersion compensators adjust the phase informationof the optical pulses in order to compensate for the chromaticdispersion in the optical fiber while appreciating the role of opticalnonlinearities in the optical fiber. Another variation that may beemployed is the optical dropping and adding of channels at citieslocated in between the two end cities. The invention disclosed herein,would find application in any of these variations, as well as others.

Traditionally, optical transport systems are deployed in networks inorder to provide connectivity among many cities on a continental orglobal basis. The selection of type and quantity of equipment is doneaccording to a traffic demand schedule, and differences in demand, orchanging demand will consequently change the optimum network design.Modern networks are characterized by large capital and operational costsand must be managed efficiently to be profitable in a competitivemarket. From a technological standpoint the efficient buildout of anetwork in a changing traffic demand environment is hampered by theflexibility of current optical transport equipment. There is a need forflexible optical transport systems that support optimal network designsunder different traffic loads.

SUMMARY OF THE INVENTION

In the present invention, improvements to an optical transport system toallow for efficient and flexible network evolution are disclosed. Morespecifically, the invention teaches a method and architecture forbypassing a terminal site without affecting existing traffic.

In one embodiment of the invention, an architecture for opticallybypassing a terminal site is taught.

In another embodiment of the invention, a method for optically bypassinga terminal site is taught.

In another embodiment of the invention, a means of upgrading a terminalsite to behave effectively like an optical add-drop (OADM) site istaught.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent invention, reference is now made to the detailed description ofthe invention along with the accompanying figures in which correspondingnumerals in the different figures refer to corresponding parts and inwhich:

FIG. 1 is a schematic illustration of a prior art terminal site with aninefficient implementation of pass through traffic.

FIG. 2 is a schematic illustration of a terminal site with pass throughtraffic managed by an optical bypass switch in accordance with theinvention.

FIG. 3 is a schematic illustration of a terminal showing the connectionlocation to the optical bypass switch in accordance with a preferredembodiment.

FIG. 4 is a schematic illustration of a terminal showing the connectionlocation to the optical bypass switch in accordance with an alternatepreferred embodiment.

FIG. 5 is a schematic illustration of a terminal showing the connectionlocation to the optical bypass switch in accordance with an alternatepreferred embodiment.

FIG. 6 is a schematic illustration of a terminal showing the connectionlocation to the optical bypass switch in accordance with an alternatepreferred embodiment.

FIG. 7 is flowchart of a method of optically bypassing a terminal sitein accordance with a preferred embodiment.

FIG. 8 is a flowchart of a method of evaluating the need for andinstalling optical splitters.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the presentinvention are discussed in detail below, it should be appreciated thatthe present invention provides many applicable inventive concepts thatcan be embodied in a wide variety of specific contexts. The specificembodiments described herein are merely illustrative of specific ways tomake and use the invention and do not delimit the scope of theinvention.

In FIG. 1 is shown a prior art block diagram of a terminal site of anoptical communications network. In FIG. 1 is shown long haul fiber pair122, terminal 110, terminal 112 and long haul fiber pair 124. Long haulfiber pair 122 and long haul fiber pair 124 are realized by cabledoptical fiber such as SMF-28 or LEAF and provide media for transmittinglong haul optical signals to adjacent network elements such as terminalsites, OADM sites, or amplifier sites. Terminal 110 and terminal 112comprise a set of line cards including transceiver cards, amplifiercards, dispersion compensation cards multiplexer-demultiplexer cards,and other functional line cards. Terminal 110 provides optical toelectrical termination of optical signals from long haul fiber pair 122.Terminal 110 also provides electrical to optical generation forelectrical signals sent on long haul fiber pair 122. Terminal 112provides optical to electrical termination from long haul fiber pair124. Terminal 112 also provides electrical to optical generation forelectrical signals sent on long haul fiber pair 124.

Also shown in FIG. 1 is local fiber patch cord pair 126 and local nodeelement 114. Local node element 114 may comprise a local terminal thatis part of a short haul, or metro system, or it may be a switch orrouter. Local fiber patch cord pair 126 is realized by a pair ofconnectorized jacketed optical fibers. A non-limiting representativelength range of local fiber patch cord pair 126 is 10 m-10 km. Localfiber patch cord pair 126 provides the transmission media for opticalsignals between terminal 110 and local node element 114.

Also shown in FIG. 1 are pass through fiber patch cord pair 130, passthrough fiber patch cord pair 132, pass through fiber patch cord pair134, pass through fiber patch cord pair 136, and pass through fiberpatch cord pair 138. Pass through fiber patch cord pair 130 is realizedby a pair of connectorized jacketed optical fibers. A non-limitingrepresentative length range of pass through fiber patch cord pair 130 is10-100 m. Pass through fiber patch cord pair 132 is realized by a pairof connectorized jacketed optical fibers. A non-limiting representativelength range of pass through fiber patch cord pair 132 is 10-100 m. Passthrough fiber patch cord pair 134 is realized by a pair of connectorizedjacketed optical fibers. A non-limiting representative length range ofpass through fiber patch cord pair 134 is 10-100 m. Pass through fiberpatch cord pair 136 is realized by a pair of connectorized jacketedoptical fibers. A non-limiting representative length range of passthrough fiber patch cord pair 136 is 10-100 m. Pass through fiber patchcord pair 138 is realized by a pair of connectorized jacketed opticalfibers. A non-limiting representative length range of pass through fiberpatch cord pair 138 is 10-100 m. The exact number of local fiber patchcord pairs and pass through fiber patch cord pairs is merelyrepresentative and non-limiting. The relative number of local fiberpatch cord pairs to pass through fiber patch cord pairs is merelyrepresentative and non-limiting. Further, the number of local fiberpatch cord pairs and pass through fiber patch cord pairs will change asthe traffic in the network changes, over the lifetime of the system.Initially, terminal 110 will drop and add more traffic to local nodeelement 114, than will be patched through to terminal 112. As thenetwork grows, however, much of the traffic will end up patched throughfrom terminal 110 to terminal 112. Modem transport equipment can supportas many as 200 channels so the cost, management and routing of patchcords becomes problematic.

The invention seeks to eliminate pass through fiber patch cords in anetwork traffic flexible manner with no impact on the initial cost ofthe system. Further, since each fiber patch cord pair is connected to atransceiver card, the cost of said card will also be reduced oreliminated due to the benefits of the invention.

In FIG. 2 is shown a schematic illustration of a terminal site with passthrough traffic managed by an optical bypass switch in accordance withone aspect of the invention. Shown in FIG. 2 are optical splitter 202,optical combiner 204, optical combiner 206 and optical splitter 208. Ina preferred embodiment, optical splitter 202 is realized by a thin filmoptical decoupler. In an alternate embodiment, optical splitter 202 isrealized by a fused optical fiber decoupler. In a preferred embodiment,optical combiner 204 is realized by a thin film optical coupler. In analternate embodiment, optical combiner 204 is realized by a fusedoptical fiber coupler. In a preferred embodiment, optical combiner 206is realized by a thin film optical coupler. In an alternate embodiment,optical combiner 206 is realized by a fused optical fiber coupler. In apreferred embodiment, optical splitter 208 is realized by a thin filmoptical decoupler. In an alternate embodiment, optical splitter 208 isrealized by a fused optical fiber decoupler.

Also shown in FIG. 2 is optical bypass switch 210 and optical bypassswitch 212. In a preferred embodiment, optical bypass switch 210 isrealized by a dynamic spectral equalizer. In a preferred embodiment,optical bypass switch 212 is realized by a dynamic spectral equalizer.Dynamic spectral equalizers are commercially available and perform threebasic functions. Firstly, dynamic spectral equalizers spectrallydecompose the DWDM wavelengths (channels) on the input fiber intophysically separate paths. Secondly, dynamic spectral equalizers providechannel by channel attenuation or extinguishing on a programmable andchangeable basis. Thirdly, dynamic spectral equalizers spectrallyrecombine the non-extinguished channels onto a single output fiber.

The signal flow path of the invention may now be understood in referenceto FIG. 2. An input DWDM signal propagating in long haul fiber pair 122towards terminal 110 is split by optical splitter 202 so that a portionof the signal continues to propagate towards terminal 110 and theremaining portion propagates into optical bypass switch 210. Withinoptical bypass switch 210, the DWDM signal is decomposed by adiffraction grating or other spectral decomposition device. Theseparated channels are subsequently attenuated. The attenuation is setso that channel powers will be compatible with those channels that willbe combined from the terminal in optical combiner 206. If a particularchannel is to be transmitted from terminal 112, optical bypass switch210 extinguishes that channel's wavelength. In normal mode of operation,if a particular channel is to be received in terminal 110 optical bypassswitch 210 extinguishes that channel's wavelength. In broadcast mode ofoperation, if a particular channel is to be received in terminal 110optical bypass switch 210 does not extinguish that channel's wavelength,however in this mode, terminal 112 may not transmit at this wavelength.The remaining channels are then recombined in optical bypass switch 210and output optical bypass switch 210. The output signal is combined withthe transmitted signals from terminal 112 in optical combiner 206.

The reverse signal flow is similar, and will now be disclosedexplicitly. An input DWDM signal propagating in long haul fiber pair 124towards terminal 112 is split by optical splitter 208 so that a portionof the signal continues to propagate towards terminal 112 and theremaining portion propagates into optical bypass switch 212. Withinoptical bypass switch 212, the DWDM signal is decomposed by adiffraction grating or other spectral decomposition device. Theseparated channels are subsequently attenuated. The attenuation is setso that channel powers will be compatible with those channels that willbe combined from the terminal in optical combiner 204. If a particularchannel is to be transmitted from terminal 110, optical bypass switch212 extinguishes that channel's wavelength. In normal mode of operation,if a particular channel is to be received in terminal 112 optical bypassswitch 212 extinguishes that channel's wavelength. In broadcast mode ofoperation, if a particular channel is to be received in terminal 112optical bypass switch 212 does not extinguish that channel's wavelength,however in this mode, terminal 110 may not transmit at this wavelength.The remaining channels are then recombined in optical bypass switch 212and output optical bypass switch 212. The output signal is combined withthe transmitted signals from terminal 110 in optical combiner 204.

In a preferred embodiment optical bypass switch 210 and optical bypassswitch 212 are combined in a single bidirectional optical bypass switchcommercially sold as a bidirectional dynamic spectral equalizer.

This architecture and method of creating optical bypass of a terminalnode allows for the recovery of expensive transceivers at a terminalsite, regardless of when the terminal was deployed. The optical bypassarchitecture may be designed and deployed for a wide variety of existingequipment in current networks. The programmability of optical bypassswitch 210 and optical bypass switch 212 eliminates detailedpre-planning of a network which leads to inefficiency.

An important aspect of this invention is that only optical splitter 202,optical combiner 204, optical combiner 206 and optical splitter 208 needbe installed with the system at initial deployment. In this manner,optical bypass switch 210 and optical bypass switch 212 can be deployedin a non-traffic effecting manner at the point in time when a sufficientamount of bypass traffic exists.

In FIG. 3 is shown a block diagram of certain components of terminal 110and their arrangement relative to long haul optical fiber pair 122,optical splitter 202 and optical combiner 204. Shown in FIG. 3 are inputfirst stage optical amplifier 310, input dispersion compensator 320,input second stage optical amplifier 312, demultiplexer 324, opticalreceiver 332 and optical receiver 334. Together, input first stageoptical amplifier 310, input dispersion compensator 320, input secondstage optical amplifier 312, demultiplexer 324, optical receiver 332 andoptical receiver 334 comprise the receiving portion of terminal 110.Also shown in FIG. 3 are output first stage optical amplifier 316,output dispersion compensator 322, output second stage optical amplifier314, multiplexer 326, optical transmitter 336 and optical transmitter338. Together, output first stage optical amplifier 316, outputdispersion compensator 322, output second stage optical amplifier 314,multiplexer 326, optical transmitter 336 and optical transmitter 338comprise the transmitting portion of terminal 110. In a preferredembodiment input first stage optical amplifier 310, input second stageoptical amplifier 312, output first stage optical amplifier 316 andoutput second stage optical amplifier 314 are realized by erbium dopedfiber amplifiers (EDFAs). Input first stage optical amplifier 310, inputsecond stage optical amplifier 312, output first stage optical amplifier316 and output second stage optical amplifier 314 function to combat theimpairment of attenuation that the optical signals encounter in longhaul fiber pair 122. In a preferred embodiment, input dispersioncompensator 320 and output dispersion compensator 322 are realized byspecialty dispersion compensating fiber. Input dispersion compensator320 and output dispersion compensator 322 function to combat theimpairment of dispersion that the optical signals encounter in fiberpair 122. In a preferred embodiment optical receiver 332 and opticalreceiver 334 are realized with semiconductor photodetectors and highspeed amplifying, filtering and decision electronics, as is well knownin the art. In a preferred embodiment optical transmitter 336 andoptical transmitter 338 are realized with semiconductor lasersmodulators, biasing and drive electronics, as is well known in the art.The number of optical receivers and optical transmitters in FIG. 1 isnot meant to be restrictive. Modern optical transport systems maycomprise 200 optical receivers and the same number of opticaltransmitters. Further, as channel counts become high, additional opticalamplifiers may also be deployed. It should also be noted that if opticalsplitter 202 and optical combiner 204 are applied to an existingterminal 110, then the internal arrangement of terminal 110 and even thepresence of the components within terminal 110 may vary.

In FIG. 3, optical splitter 202 and optical combiner 204 are locatedoutside and in close proximity to terminal 110. This location offerslogistical advantages including ease of operation and installation. Inalternate embodiments of this invention, alternate locations providealternate advantages.

Referring now to FIG. 4 for an alternate preferred embodiment of theinvention, optical splitter 202 and optical combiner 204 are located inalternate locations internal to terminal 110. In this embodiment of theinvention, input first stage optical amplifier 310, input second stageoptical amplifier 312, output first stage optical amplifier 316 andoutput second stage optical amplifier 314 function to combat theapproximate 3dB loss associated with optical splitter 202 and opticalcombiner 204.

Referring now to FIG. 5 for an alternate preferred embodiment of theinvention, optical splitter 202 is located internal to terminal 110after input first stage optical amplifier 310, input second stageoptical amplifier 312 to allow input first stage optical amplifier 310,input second stage optical amplifier 312 to amplify the weak inputoptical signal arriving at terminal 110. Optical combiner 204 is locatedafter output second stage optical amplifier 314. This embodiment allowsfor the correct dispersion compensation amount to be applied to theoptical signals.

Referring now to FIG. 6 for an alternate preferred embodiment of theinvention, optical splitter 202 is located internal to terminal 110after input dispersion compensator 320 and before input second stageoptical amplifier 312. In this embodiment optical combiner 204 islocated internal to terminal 110 after output dispersion compensator 320and before output second stage optical amplifier 312. This embodimentallows for the correct dispersion compensation amount to be applied tothe optical signals, with the smallest impact to system performance andno impact to terminal optical loss budget.

In FIG. 7 is shown a flow chart of a method for optically bypassing aterminal site is taught in accordance with the invention. In step 710,terminal 110 is installed at a terminal site in an optical network. Instep 715, Optical splitter 202 and optical combiner 204 are installed inor in close proximity to terminal 110. In step 720, add channels to thenetwork as traffic demand grows. In step 725, the decision is madewhether optical bypass switch 210 and optical bypass switch 212 arejustified economically. This decision is based on capital costs anddiscounted operational costs at the time of the decision. If thedecision is negative, then no bypass switch is installed, untiladditional channels are added. If the decision is positive, then opticalbypass switch 210 and optical bypass switch 212 are installed in step730. In step 735, transceiver and other hardware may be recovered andredeployed elsewhere in the network.

FIG. 8 shows a flow chart of a method for evaluating the need forinstalling optical splitters at a terminal site in accordance with theinvention for which optical bypass was not originally envisioned. Instep 810, terminal 110 is installed at a terminal site on an opticalnetwork. In step 815, channels are added in the normal course to theoptical network as traffic grows. At step 820 an evaluation is made ofthe necessity for a splitter and optical bypass system. The decision isbased on capital costs and discounted operational costs at the time ofthe decision. If the decision is negative, then no splitter isinstalled, until additional channels are added. If the decision ispositive, then the splitter and optical combiner are installed in step830. In step 835, the optical bypass switch is installed. In step 840transceiver and other hardware may be recovered and redeployed elsewherein the network.

While this invention has been described in reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

1. A terminal for use in an optical bypass system comprising: an opticalsplitter connected to an incoming optical fiber; a first amplifierconnected to the optical splitter; at least one optical receiverconnected to the optical amplifier; an optical combiner connected to anoutgoing optical fiber; a second amplifier connected to the opticalcombiner; at least one optical transmitter connected to the secondamplifier.
 2. The terminal of claim 1 wherein the first amplifier is amulti stage amplifier.
 3. The terminal of claim 2 wherein a dispersioncompensation module is interposed between the stages of the multi stageamplifier.
 4. The terminal of claim 1 wherein the second amplifier is amulti stage amplifier.
 5. The terminal of claim 4 wherein a dispersioncompensation module is interposed between the stages of the multi stageamplifier.
 6. The terminal of claim 1 wherein the optical splitter isconnected to a first bypass switch.
 7. The terminal of claim 6 whereinthe first bypass switch is a dynamic spectral equalizer.
 8. The terminalof claim 6 wherein the optical combiner is connected to a second bypassswitch.
 9. The terminal of claim 8 wherein the second bypass switch is adynamic spectral equalizer.
 10. A terminal for use in an optical bypasssystem comprising: a first amplifier connected an incoming opticalfiber; an optical splitter connected to the first amplifier; at leastone optical receiver connected to the optical splitter; a secondamplifier connected to an outgoing optical fiber; an optical combinerconnected to the second amplifier; at least one optical transmitterconnected to the optical combiner.
 11. The terminal of claim 10 whereinthe first amplifier is a multi stage amplifier.
 12. The terminal ofclaim 11 wherein a dispersion compensation module is interposed betweenthe stages of the multi stage amplifier.
 13. The terminal of claim 10wherein the second amplifier is a multi stage amplifier.
 14. Theterminal of claim 13 wherein a dispersion compensation module isinterposed between the stages of the multi stage amplifier.
 15. Theterminal of claim 10 wherein the optical splitter is connected to afirst bypass switch.
 16. The terminal of claim 15 wherein the firstbypass switch is a dynamic spectral equalizer.
 17. The terminal of claim15 wherein the optical combiner is connected to a second bypass switch.18. The terminal of claim 17 wherein the second bypass switch is adynamic spectral equalizer.
 19. A terminal for use in an optical bypasssystem comprising: a first amplifier connected to an incoming opticalfiber; an optical splitter connected to the first amplifier; at leastone optical receiver connected to the optical splitter; an opticalcombiner connected to an outgoing optical fiber; a second amplifierconnected to the optical combiner; at least one optical transmitterconnected to the second amplifier.
 20. The terminal of claim 19 whereinthe first amplifier is a multi stage amplifier.
 21. The terminal ofclaim 20 wherein a dispersion compensation module is interposed betweenthe stages of the multi stage amplifier.
 22. The terminal of claim 19wherein the second amplifier is a multi stage amplifier.
 23. Theterminal of claim 22 wherein a dispersion compensation module isinterposed between the stages of the multi stage amplifier.
 24. Theterminal of claim 19 wherein the optical splitter is connected to afirst bypass switch.
 25. The terminal of claim 24 wherein the firstbypass switch is a dynamic spectral equalizer.
 26. A terminal for use inan optical bypass system comprising: an incoming multi stage amplifierhaving at least an incoming first stage and an incoming second stageconnected to an incoming optical fiber; a first dispersion compensationmodule connected to the incoming first stage; an optical splitterconnected to the first dispersion compensation module and to theincoming second stage; at least one optical receiver connected to theincoming second stage; an outgoing multi stage amplifier having at leastan outgoing first stage and an outgoing second stage connected to anoutgoing optical fiber; an optical combiner connected to the outgoingsecond stage; a second dispersion compensation module connected to theoptical combiner; the outgoing first stage connected to the dispersioncombiner; at least one optical transmitter connected to the outgoingfirst stage.
 27. A terminal for use in an optical bypass systemcomprising: an incoming multi stage amplifier having at least anincoming first stage and an incoming second stage connected to anincoming optical fiber; a first dispersion compensation module connectedto the incoming first stage; an optical splitter connected to the firstdispersion compensation module and to the incoming second stage; atleast one optical receiver connected to the incoming second stage; anoutgoing multi stage amplifier having at least an outgoing first stageand an outgoing second stage connected to an outgoing optical fiber; anoptical combiner connected to the outgoing second stage; a seconddispersion compensation module connected to the optical combiner; theoutgoing first stage connected to the dispersion combiner; at least oneoptical transmitter connected to the outgoing first stage wherein theoptical splitter is connected to a first bypass switch.
 28. A terminalfor use in an optical bypass system comprising: an incoming multi stageamplifier having at least an incoming first stage and an incoming secondstage connected to an incoming optical fiber; a first dispersioncompensation module connected to the incoming first stage; an opticalsplitter connected to the first dispersion compensation module and tothe incoming second stage; at least one optical receiver connected tothe incoming second stage; an outgoing multi stage amplifier having atleast an outgoing first stage and an outgoing second stage connected toan outgoing optical fiber; an optical combiner connected to the outgoingsecond stage; a second dispersion compensation module connected to theoptical combiner; the outgoing first stage connected to the dispersioncombiner; at least one optical transmitter connected to the outgoingfirst stage wherein the first bypass switch is a dynamic spectralequalizer.